The invention relates to a flat tube for the circulation of a fluid in a heat exchanger, especially a radiator for cooling the engine powering a motor vehicle, formed by a strip of sheet metal folded so as to define a peripheral wall separating the interior of the tube from the exterior and an intermediate wall or spacer mechanically reinforcing the tube and dividing the interior thereof into two longitudinal flow channels which are open at at least one first end of the tube, the mechanical connection between the peripheral wall and the spacer being provided partly by the continuation of the material of the strip and partly by brazing, the tube including a body which features a substantially constant elongate cross section.
In order to produce a heat exchanger, such tubes are gathered together into a tube array in which they are aligned in one or more rows and separated from one another by fins which furthermore enhance the exchange of heat between the fluid flowing in the tubes and an airflow flowing between them and sweeping over the fins. The channels of each tube open out at the first end thereof into a fluid chamber, one wall of which consists of a collector plate or collector pierced with holes through which the end zones of the tubes pass in a leaktight fashion.
In the known heat exchangers thus constituted, the cross section of the tubes is substantially constant over their entire length. In the direction of the length of this cross section, the overall size of the exchanger is therefore related to that of the set of tubes, the fluid chamber necessarily extending, in this direction and both ways, beyond the single row or the set of rows of tubes.
This constraint constitutes a drawback, especially in motor-vehicle construction, where the space for housing the components is measured out ever more sparingly.
The object of the invention is to remedy this drawback, by reducing the total overall size of the heat exchanger for a given size of the array of tubes.
The invention especially envisages a tube of the type defined in the introduction, and provides, moreover, for it to include at least one head region extending between its body and the said first end, in which the said peripheral wall, but not the spacer, is deformed in such a way as to dilate the channels in the direction of the width of the said cross section and to shrink them again towards the spacer in the direction of the length of the cross section.
The shrinking of the channels towards the spacer in the head region has the effect that, by comparison with the overall size of the tube array in the direction of the length of the cross section of the tubes, the overall size of the head region, and consequently the minimum overall size of the fluid chamber, which interacts with it, are reduced. The absence of deformation of the spacer allows it to keep its reinforcing function and, as appropriate, its function of leaktightness between the two channels.
Complementary or alternative optional characteristics of the invention are set out below:
the head region comprises an end zone of substantially constant cross section corresponding to a maximum deformation and a transition zone linking the end zone to the body and in which the cross section changes progressively between those of the end zone and of the body.
in the head region, the width of the said cross section varies progressively, from the spacer and on either side of it, from a minimum value to a maximum value.
the flow channels are open at the second end of the tube, and the latter further includes a second head region extending between its body and its second end, the peripheral wall being deformed in the same way in the two head regions.
the spacer is formed by two marginal zones of the said strip, brazed mutually face-to-face, the opposite edge faces of the strip, adjacent respectively to these two zones, coming opposite the inner face of the peripheral wall to which they are brazed.
the strip is folded into a configuration which is symmetric with respect to the general plane of the spacer.
A further subject of the invention is a heat exchanger, especially a cooling radiator for the engine powering a motor vehicle, comprising at least one row of tubes as defined above, which are aligned in the direction of the width of their cross section, a fluid chamber being associated with the head region or with each head region of the set of tubes, a wall or collector plate of this fluid chamber being pierced by holes through which pass the end zones of the tubes, in such a way that the channels open out into the fluid chamber.